1. Field of the Invention
The present invention relates generally to a scanning tunneling microscope (STM) and more particularly to a scanning tunneling microscope including an optical system for optically observing an object.
2. Description of the Related Art
A scanning tunneling microscope (STM) was proposed by Binnig et al. in 1982 in U.S. Pat. No. 4,343,993. A sharply pointed probe is approached to the surface of an object, and a bias voltage is applied across the probe and the object. Consequently, a tunnel current flows between the probe and the object. It is known that the distance between the probe and the object varies by about one Angstrom, and that the tunnel current varies by about one order of magnitude. The STM utilizes the property of the tunnel current, thereby measuring the surface configuration of the object in an atomic level. For example, the probe is caused to scan the surface of the object, while the distance between the object and the probe is controlled to keep the value of the tunnel current constant. The position of the probe is recorded to obtain an image reflecting the surface configuration of the object in an Angstrom level.
The resolution of the STM is very high. Thus, the STM is not suitable for observation of a broad area on an object with low magnifying power, for selecting an observation region. Under the situation, there has been proposed an STM in which an optical microscope is built (hereinafter, called "optical microscope-built-in STM"). This type of STM includes an observation optical system capable of optically observing the surface of the object.
In the optical microscope-built-in STM, a conventional optical microscope is generally employed. For example, such an optical microscope has a revolver with a plurality of objective lenses. The objective lens is replaced by rotating the revolver. According to an optical microscope-built-in STM, STM units (each including a probe and a probe scan mechanism), in place of the objective lenses, are attached to the revolver.
In this type of optical microscope-built-in STM, an elevation stage for mounting an object table thereon and an STM unit are supported by a microscope body only at one side. Thus, the STM is easily affected by external vibration, and there is a relative displacement (a phase difference of vibration) between the probe and the object. In addition, space is present between the probe and the object, the STM is affected by air flow, external electric noise, and magnetic noise.